This invention relates to an ignition coil device for igniting a fuel mixture in an internal combustion engine having a winding element mounted on a coil winding cylindrical in shape which may be connected to a spark plug, a sheet metal jacket circumferentially enclosing the winding element with coil winding, and an elastic insulating element in the form of a hollow cylinder which is mounted on a section of the winding element facing the spark plug for insulation against high voltage.
Rod ignition coils are used to generate high voltage for igniting a fuel mixture in an internal combustion engine. A rod ignition coil represents a high-voltage transformer whose magnetic circuit consists of a main core enclosed in a secondary or primary coil, in which core there may be an air gap, and of ground legs or yoke elements. In the case of rod ignition coils the magnetic ground is completed by the housing made up of bent electric sheeting. The primary winding of the rod ignition coil is supplied with suitable current by way of control electronics. The control electronics interrupt the primary current, as a result of which a high-voltage is generated on the secondary side to impinge on an ignition coil mounted on the rod ignition coil.
The rod ignition coil is normally cast in the interior of the housing by injection of an electrically insulating sealing compound. This casting serves the purpose of immobilizing in their desired position the components mounted inside the housing, such as the soft magnetic core and the coil element with primary and secondary coil, without the need for additional retaining means. In order to prevent interior stresses caused by the casting compound, the inner wall of the housing may be coated with an elastic medium and the gap between the elastic medium and the components mounted inside the housing may be coated with an electrically insulating resin. Consequently, thermal expansion which may result in formation of cracks in the interior of the housing may be prevented.
In order to avoid this additional production engineering expense of elastic coating, German patent DE 199 27 820 C1 discloses hollowing out of the casting compound inside the rod ignition coil body in the area between the outer winding and the housing. As a result, the winding should be able to undergo thermal expansion during heating so that internal stresses do not occur. Provision is made such that a connecting section of flexible material impervious to high voltage is used which covers the rod ignition coil and the spark plug; this connecting section has on the ignition coil side a coupling section in the area of which the housing and at least one of the two coil elements are elastically interconnected. The elastomer material of the connecting section is sprayed around and mounted around one of the two coil elements in the area between housing and coil element exterior. A section absorbing expansion or stresses is consequently formed at the point at which the outer annular space is formed. It is also specified in this document that an elastomer connection empties directly into the area between the housing and the outer coil element, so that the two components are interconnected by way of the elastic medium. The elastic medium is thus inserted below the housing. As a result, the housing is both centered and sealed.
Sealing of cavities in the rod ignition coil is disclosed, for example, in German patent DE 197 02 438 C2.
Sealing of the primary coil from environmental effects is needed in particular to prevent corrosion of the primary winding. Consequently, the effect of sealing from moisture, fouling, and reagents of all kinds is to be achieved.